Negative-pressure ventilation

Figure 3-5 The difference between a positive and a negative pressure ventilation system. The negative pressure system ensures that contaminants do not leak into workplace environments.

Negative pressure ventilators (the old iron lung) are not used anymore. 

Ventilators are either negative-pressure or positive-pressure. Negative-pressure ventilation involves directing air directly into the lungs, and positive-pressure ventilation involves directing air into the trachea. Some ventilators require intubation, the placement of a tube into the trachea from the nose or mouth. Ventilation requiring intubation is typically used for patients who will require ventilation for a protracted period. Other ventilators work with a breathing mask that can be placed over the mouth and nose. With the increase in respiratory-related sleep disorders (such as obstructive sleep apnea), use of two positive airway pressure systems—continuous positive airway pressure (CPAP) and bilevel positive pressure ventilators (BiPAP)—has become very common. 

The most complete European data on the use of HMV has been reported recently as the Eurovent study, a survey of long-term ventilator use conducted in 16 countries (15). In this survey, home ventilation was defined as ventilatory assistance for three months or more. Those receiving other forms of ventilation, such as rocking beds, negative-pressure ventilation, and phrenic nerve stimulation, were included. A total of 483 surveys were sent to the centers prescribing HMV in the 16 countries, with 329 centers (68%) responding. The numbers of patients and prevalence rates were estimated for each country. As noted in Table 3, there was a wide variation in the prevalence of HMV in Europe, ranging from 0.1/ 100,000 population in Poland to 17/100,000 in France. The survey identified a total of 21,526 VAIs and estimated the prevalence of HMV to be 6.6/100,000 population in Europe. 

Negative pressure ventilators apply subatmospheric pressure outside the chest to inflate the lungs. The negative pressure causes the chest wall to expand and the pressure difference between the lungs and the atmosphere causes air to flow in. 

Corrado A, Gorrino M. Long-term negative pressure ventilation. Respir Care Clin 2002 8 545-557. 

Goldstein RS, Molotiu N, Skrastins R, et al. Reversal of sleep induced hypoventilation and chronic respiratory failure by nocturnal negative pressure ventilation in patients with restrictive ventilatory impairment. Am Rev Respir Dis 1987 135 1049-1055. 

Scano G, Gigliotti F, Duranti R, et al. Changes in ventilatory muscle function with negative pressure ventilation in patients with severe COPD. Chest 1990 97(2) 322-327. 

Cropp A, DiMarco AF. Effects of intermittent negative pressure ventilation on respiratory muscle function in patients with severe chronic obstructive pulmonary disease. Am Rev Respir Dis 1987 135(5) 1056-1061. 

Celli B, Lee H, Criner G, et al. Controlled trial of external negative pressure ventilation in patients with severe chronic airflow obstruction. Am Rev Respir Dis 1989 140(5) 1251-1256. 

Shapiro SH, Ernst P, Gray-Donald K, et al. Effect of negative pressure ventilation in severe chronic obstructive pulmonary disease. Lancet 1992 340(8833) 1425-1429. 

Pressure-cycled machines predominated in 2002 (70.6% of the total) and only a very small percentage of patients (0.005%) were still using forms of negative pressure ventilators. Ventilation was performed via a tracheostomy in just 13% of the overall survey population and the patients with NMD accounted for most of these. Tracheostomy ventilation was more common in France, Greece, Italy, and Belgium and probably reflects local expertise in this area (16). 

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